To my knowledge these two actually haven't been proven for sure incompatible. Unless of course I'm out of the loop again
The only breeding I know of that produced eggs was het to het done by SK years ago that only had 5 eggs and no axanthics.....so they might have just missed?
I know that talking to Graziani and Micheal Cole (python hunters) at Tinley 2 years ago they thought VPI and SK would end up being compatible.
Hope that helpsIf I had a VPI girl I'd give it a try